Storm Sewer Sediment-Water Interface Exchange And Release Of Phosphorus And Heavy Metals Research The Law

The experiment samples of this study is Storm sewer sediment collected from an oldresidential area on Northern Lishi road, on Aug.3th2011that is the5th continuous sunnyday after heavy rainy, and the runoff during next rainy mid-term at the same position;under different external conditions applying to simulation in the lab, PH value, temp, DOand flow rate are studied about affection on TP, Zn, Cu, Pb, Cr and Cd releasing onsurface between pipe sediment and water; and then, the exchange rate of PT, An, Cu, Pb,Cr, Cd and sediment water surface is calculated by continuous function method.Determine the environment factors that effect P and heavy metals releasing from waterpipe sediment, provide theoretical evidence for controlling the2nd releasing of overlyingwater from pipe sediment, and setting up polluting material releasing and moving models,finally, evaluate the P and heavy metals releasing volume under different exchange ratefor a segment of rainwater pipe under different flow rate according to the experimentresult, and provide reference for calculating discharged receiving water body pollutionload.According to experiment studying, it concludes below result:1. The main factor of effecting P&heavy metal exchanging and releasing at thesurface of rainwater pipe sediment and water（1） Acid and alkali environment are both promoting P and heavy metal releasing,and acid environment is performing more apparent releasing; the nearer to neutralenvironment, the less affection; the P and heavy metal accumulation releasing max. valueand its average concentration from overlying water is performing parabola relationshipwith PH value;（2） Within temperature getting arising, the P and heavy metal releasing is goingstronger accordingly from sediment; the average concentration of overlying water andaccumulation releasing max. value of sediment are both having linear relationship withtemperature;（3） The dissolved oxygen performing a great effect on P releasing, the sedimentperforms obviously P releasing on the condition of Hypoxia and anaerobic, a little Preleasing at the beginning of good oxygen condition, and no obvious P releasing in theleft time; within the higher dissolved oxygen content, average concentration of overlyingwater TP and P accumulation releasing max. value of sediment is going down as index;because Chemical speciation different content and percentage of oxidisable and redoxstate, the different effect on heavy metal releasing from dissolved oxygen concentration,and it’s almost the same releasing law of Zn, Cu, Pb and Cr, good oxygen environmentpromoting its releasing to overlying water, absorbing heavy metal from overlying waterunder poor oxygen environment, but Cd releases in the poor oxygen environment, and more apparent releasing within dissolved oxygen concentration lowing; in which, theaverage dissolved concentration of Zn, Cu, Pb and Cr is performing parabola linerelationship with dissolved oxygen concentration, max. releasing volume havingLogarithmic relationship with dissolved oxygen concentration, average concentration ofCd is performing index relationship with max. releasing volume and dissolved oxygenconcentration;（4） Flow rate is the main factor that affects the releasing from P and heavy metal inthe rainwater pipe to overlying rain water. Within the higher flow rate, the sedimentobviously releases more volume P and heavy metal; within higher flow rate, TP averageconcentration from overlying water is performing index increasing comparing with max.volume from overlying water P; average concentration and max. releasing rate of Zn, Cu,Pb and Cr is performing parabola relationship with flow rate; average concentration andmax. releasing rate is performing a linear relationship with flow rate.2. The exchange rate of phosphorus and heavy metals under various flow rates onthe sediment-water interface（1） The average release rates of phosphorus before the equilibrium betweensediments and overlying water are0.62mg·m^-2·min^-1、1.04mg·m^-2·min^-1、2.51mg·m^-2·min^-1、2.85mg·m^-2·min^-1、4.09mg·m^-2·min^-1respectively, when DO is7mg/L, pHequal to8, the temperature is26℃and the flow rate is0.3m/s,0.5m/s,0.7m/s,0.9m/s,1.1m/s；（2） The average release rates of Zn、Cu、Pb、Cr、Cd from sediment before theequilibrium between sediments and overlying water are in Table3-2, when DO is7mg/L, pH equal to8, the temperature is26℃and the flow rate is0.3m/s,0.5m/s,0.7m/s,0.9m/s,1.1m/s；3. Take a stormwater pipeline for an example to estimate the total amount of releaseof phosphorus and heavy metals under different flow rates from sedimentsTake a rain water pipeline which was located in an old residential area, and had a500m long,300mm diameter for an example, to estimate the total amount of release ofphosphorus and heavy metals under different flow rates from sediments, The results canbe seen in Table2-16. The results may be representative of the total release when theduration of ainfall are greater than or equal to2h, strictly speaking, it is the total releasewhen the duration of ainfall are greater than or equal to the equilibration time.